Clinical development of therapies targeting TGFβ: current knowledge and future perspectives

Transforming growth factor beta (TGFβ) is a pleiotropic cytokine that plays a key role in both physiologic and pathologic conditions, including cancer. Importantly, TGFβ can exhibit both tumor-suppressive and oncogenic functions. In normal epithelial cells TGFβ acts as an antiproliferative and differentiating factor, whereas in advanced tumors TGFβ can act as an oncogenic factor by creating an immune-suppressive tumor microenvironment, and inducing cancer cell proliferation, angiogenesis, invasion, tumor progression, and metastatic spread. A wealth of preclinical findings have demonstrated that targeting TGFβ is a promising means of exerting antitumor activity. Based on this rationale, several classes of TGFβ inhibitors have been developed and tested in clinical trials, namely, monoclonal, neutralizing, and bifunctional antibodies; antisense oligonucleotides; TGFβ-related vaccines; and receptor kinase inhibitors. It is now >15 years since the first clinical trial testing an anti-TGFβ agent was engaged. Despite the promising preclinical studies, translation of the basic understanding of the TGFβ oncogenic response into the clinical setting has been slow and challenging. Here, we review the conclusions and status of all the completed and ongoing clinical trials that test compounds that inhibit the TGFβ pathway, and discuss the challenges that have arisen during their clinical development. With none of the TGFβ inhibitors evaluated in clinical trials approved for cancer therapy, clinical development for TGFβ blockade therapy is primarily oriented toward TGFβ inhibitor combinations. Immune checkpoint inhibitors are considered candidates, albeit with efficacy anticipated to be restricted to specific populations. In this context, we describe current efforts in the search for biomarkers for selecting the appropriate cancer patients who are likely to benefit from anti-TGFβ therapies. The knowledge accumulated during the last 15 years of clinical research in the context of the TGFβ pathway is crucial to design better, innovative, and more successful trials.

Population Pharmacokinetic Analysis of Bintrafusp Alfa in Different Cancer Types

INTRODUCTION

Bintrafusp alfa, an innovative first-in-class bifunctional fusion protein composed of the extracellular domain of the TGF-βRII receptor (a TGF-β "trap") fused to a human IgG1 monoclonal antibody blocking programmed death ligand 1, has shown promising antitumor activity and manageable safety.

METHODS

To support the dosing strategy for bintrafusp alfa, we developed a population pharmacokinetics model using a full covariate modeling approach, based on pharmacokinetic and covariate data from 644 patients with various solid tumors who received bintrafusp alfa intravenously in two clinical studies.

RESULTS

A two-compartmental linear model best described bintrafusp alfa concentrations, and no time-varying clearance was identified. Using this model, the estimated clearance was 0.0158 l/h (relative standard error, 4.1%), and the central and peripheral volume of distribution were 3.21 l (relative standard error, 3.2%) and 0.483 l (relative standard error, 9.8%), respectively. The estimated mean elimination half-life of bintrafusp alfa was 6.93 days (95% CI 4.69-9.65 days). Several intrinsic factors (bodyweight, albumin, sex, and tumor type) were found to influence bintrafusp alfa pharmacokinetics, but none of these covariate effects was considered clinically meaningful and no dosage adjustments are recommended. Notably, simulations from the model suggested less variability in exposure metrics with flat dosing versus weight-based dosing.

CONCLUSIONS

Pharmacokinetic analysis of bintrafusp alfa supports the use of a flat dose regimen in further clinical trials (recommended phase 2 dose: 1200 mg every 2 weeks).

TRIAL REGISTRATION

ClinicalTrials.gov identifiers: NCT02517398 and NCT02699515.

FUNDING

Merck Healthcare KGaA as part of an alliance between Merck Healthcare KGaA and GlaxoSmithKline.

Knowing the tumour microenvironment to optimise immunotherapy

Effective immunotherapy requires thorough knowledge of the tumour microenvironment. Indeed, the interplay among the immune system, the tumour and treatment is conditioned by the composition of the tumour microenvironment. In addition, it must be taken into account that homeostasis of the tumour microenvironment is highly dynamic and changes rapidly in function of many factors, such as inflammation, hypoxia, tumour volume, all of which change over time, and the effect of treatments. All these elements interact with each other and with conditions related to the tumour (i.e. mutational load, rate of clonal and subclonal mutations) and to host (life style, diet, obesity, age). All these factors as well as their interplay, affect the response to immunotherapy. The target of this short review is to summarise some of the major aspects that impact the homeostasis of the tumour microenvironment and how its structure can drive treatment choice.